Solution-based Synthesis Of Functional (Oxy) Fluorides And Its Characterizations

Recently, (oxy)fluoride functional materials have aroused extensive research interest due to their potential applications in superconductivity, magnetic material, catalyst, luminescence materials and so on. In this dissertation, the aim is that attentions are paid to the preparation of (oxy)fluorides based on solution synthesis routes. The optimum routes are confirmed through the optimizing the reaction processes and various experimental conditions. The properties of as prepared functional (oxy)fluoride materials are measured. In order to prepare (oxy)fluorides with excellent performance, the relations between the structure, morphology and the physical properties are also investigated. The main contents of the dissertation are as follows:1. Using NH₄HF as fluorine source, Sr₂CuO₃ and NdSr₂Cu₂O_6-δ have been successfully fluorinated through a solvethermal method. The absolute ethanol as a solvent can avoid the failure caused by the effect that copper-based oxides are sensitive to aqueous solution. An optimized preparation condition was obtained, by performing control experimental conditions. Structure analysis reveals that after low temperature treatment, their structure changed into metastable copper-based oxyfluorides. Magnetic measurement was carried out to investigate the superconductivity transformation temperature of the products. The results reveal that the transformation temperature of Sr₂Cu(O,F)_4+δ appears at 38k, while NdSr₂Cu₂(O,F)_6+δ exhibits paramagnetic property. It isn't found that the fluoridation of copper-based oxide has been reported by the solvothermal route. The result is better than other methods using NH₄HF as fluorine source.2. K₂TiF₆,K₂TiOF₄,K₃TiOF₅ and K₇Ti₄O₄F₇ micro-crystals have been successfully synthesized through solvethermal routes, using Ti or TiO₂ as starting materials. Through investigating the effects of different solvents in the synthesis, it is found that the solvents are key role to the formation of these phases. The characterizations of as prepared samples reveal that the BET surface areas of these products are very small and they possess strong absorption in UV range. Especially, K₂TiOF₄ K₂TiOF₄ additionally shows a strong absorption around visible region. The photocatalytic activities of these products were studied. The results reveal that these products show excellent photocataytic performance for degradation of RhB under UV light irradiation. It should be noted that K₂TiOF₄ has the best photocatalytic activities and its ability to degrade RhB exceeds P25(TiO₂). To further improve the photocatalytic activities of K₂TiOF₄, nanostructures of K₂TiOF₄ have been prepared. The octahedrons, spheres, rods and hollow spheres of K₂HOF₄ were obtained by controlling the experimental parameters. The effects of pH value on the formation of the product have been also investigated. The optimal pH value is 7-8. The BET areas of nanostructural products increase obviously. The results of photocatalytic experiments reveal that K₂TiOF₄ hollow structure with higher surface area exhibit better photocatalytic performance.3. Shape-controlled synthesis of perovskite KMnF₃ has been carried out through a PEG-assisted hydrothermal method. Polyhedron microcrystal, microsphere, hollow sphere of the product have been obtained by changing the reaction conditions. An Ostwald process has been proposed to explain the formation mechanism of the Polyhedron microcrystal, microsphere and hollow sphere by the reaction temperature, time, the concentration and type of PEG, which is a key role to form three micro-structures. Studies of the photophysical properties of the polyhedral microcrystals, micro-spheres and hollow spheres reveal that they are excellent luminescence materials with an excellent absorption.Nanostructure of BaF₂ has been solvothermally prepared using DMF as a solvent. The morphology evolution is from the individual nanoparticals aggregating the quadrate microflakes, v/hich was investigated through the reaction time. Photoluminescence of the nanoparticles has been compared with that of BaF₂ block, and it is a better performance for the former. The blue-shift and broadening effect are all presented in the absorption spectrum for the nanoparticles of BaF₂...